My Add-on Panel / Window / Tab is missing
It is likely that you have an add-on that is not working as it should. Try looking at your /Users/[username]/Library/Application Support/Blender/ folder. If you find the add-on that you suspect might be the issue in the scripts folder of your version folder try removing it. You could delete the entire folder with your current version number(maybe backup it first) to restore the default user preferences. It should be recreated the next time you save user preferences.